RESTful API for GitHub Webhook

[bbangert]

For Plans to be added/run after a PR is put-up, a REST API endpoint for their webhook call needs to be added.

• [ ] Add db field for Project to indicate valid github repo, and whether to run off tags or PR's
• [ ] Load Plan from PR repo
• [ ] Wait until Docker Hub has the needed docker containers/tags for the steps defined
• [ ] Run Plan
• [ ] Return Plan & Step UUID's